different heights above the surface of the ocean.

A great number of local circumstances cause the produce of evaporation
to vary; it changes in proportion as more or less shade covers the
basin of the waters, with their state of motion or repose, with their
depth, and the nature and colour of their bottom; but in general
evaporation depends only on three circumstances, the temperature, the
tension of the vapours contained in the atmosphere, and the resistance
which the air, more or less dense, more or less agitated, opposes to
the diffusion of vapour. The quantity of water that evaporates in a
given spot, everything else being equal, is proportionate to the
difference between the quantity of vapour which the ambient air can
contain when saturated, and the quantity which it actually contains.
Hence it follows that the evaporation is not so great in the torrid
zone as might be expected from the enormous augmentation of
temperature; because, in those ardent climates, the air is habitually
very humid.

Since the increase of agricultural industry in the valleys of Aragua,
the little rivers which run into the lake of Valencia can no longer be
regarded as positive supplies during the six months succeeding
December. They remain dried up in the lower part of their course,
because the planters of indigo, coffee, and sugar-canes, have made
frequent drainings (azequias), in order to water the ground by
trenches. We may observe also, that a pretty considerable river, the
Rio Pao, which rises at the entrance of the Llanos, at the foot of the
range of hills called La Galera, heretofore mingled its waters with
those of the lake, by uniting with the Cano de Cambury, on the road
from the town of Nueva Valencia to Guigue. The course of this river
was from south to north. At the end of the seventeenth century, the